Corrected entry: Gibbs will break a mobile phone (generally in the office), and be given a brand new one by Tony. No one ever notes the new number or passes it on to those who need to know it, but Gibbs can still be called by anyone, especially from their speed dial.

Correction:It can be safely assumed that the number is distributed off camera. It's not necessary to show them giving out a new number. Besides, it's also possible to assign and activate the same number to more than one phone.